The present invention relates to a semiconductor device and a method for producing the same, in particular, a high dielectric constant film used for a gate insulating film.
With recent technological advance with respect to high integration and high speed in semiconductor devices, miniaturization of MOSFETs has been under development. When the thickness of a gate insulating film is being reduced to achieve the miniaturization, problems such as an increase of a gate leak current due to tunneling current are caused. In order to suppress this problem, there has been research on an approach to increase a physical thickness while realizing a small SiO2 equivalent thickness (hereinafter, referred to as xe2x80x9cEOTxe2x80x9d) by using gate insulating films made of high dielectric constant material such as hafnium oxide (HfO2) and zirconium oxide (ZrO2) (hereinafter, referred to as xe2x80x9chigh-k gate insulating filmsxe2x80x9d).
For example, a method for forming a conventional high-k gate insulating film described in U.S. Pat. No. 6,013,553 is as follows. First, an oxide layer such as a SiO2 layer is formed on a silicon substrate, and then a metal film made of zirconium or hafnium is deposited on the oxide layer by sputtering or plasma CVD. Thereafter, the metal film is subjected to an oxynitridation treatment with gas such as NO to form a high-k gate insulating film made of zirconium oxynitride (ZrOxNy) or hafnium oxynitride (HfOxNy).
However, in the conventional high-k gate insulating film, when heat history is applied by a high temperature treatment during the production process, the high dielectric constant material constituting the gate insulating film is crystallized, so that the electrical conductivity via the resultant crystal grain boundaries or the defect level increases leak current. That is to say, the thermal stability of the conventional high-k gate insulating film is insufficient.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a semiconductor device employing a thermally stable gate insulating film having a high relative dielectric constant.
In order to achieve the object, a semiconductor device of the present invention includes a gate insulating film formed on a substrate; and a gate electrode formed on the gate insulating film, and the gate insulating film includes a high dielectric constant film containing a metal, oxygen and silicon; and a lower barrier film formed below the high dielectric constant film and containing the metal, oxygen, silicon and nitrogen.
According to the semiconductor of the present invention, the high dielectric constant film constituting the gate insulating film contains silicon, so that the high dielectric constant film is prevented from being crystallized by a high temperature treatment in the production process (e.g., a heat treatment for activating impurities at about 900xc2x0 C.). Therefore, in a finished semiconductor device, the high dielectric constant film remains mostly amorphous, so that leak current can be suppressed from occurring in the high-k gate insulating film. Consequently, the thermal stability of the high-k gate insulating film can be improved, and therefore a semiconductor device having excellent heat resistance can be realized, and the process margin in the production of a semiconductor device can be increased.
According to the semiconductor of the present invention, the lower barrier film is present below the high dielectric constant film in the gate insulating film, so that the high dielectric constant film can be prevented from reacting with the substrate. Moreover, the lower barrier film contains the same metal as in the high dielectric constant film, so that the relative dielectric constant of the lower barrier film can be increased, and thus the relative dielectric constant of the entire gate insulting film can be increased.
In the semiconductor device of the present invention, it is preferable that the gate insulating film includes an upper barrier film formed above the high dielectric constant film, and the upper barrier film contains the metal, oxygen and nitrogen.
This prevents the gate electrode material and the high dielectric constant film material from being diffused to each other. Moreover, the upper barrier film contains the same metal as in the high dielectric constant film, so that the relative dielectric constant of the upper barrier film can be increased, and thus the relative dielectric constant of the gate insulting film as a whole can be increased.
In the semiconductor device of the present invention, it is preferable to satisfy
0.23xe2x89xa6y/(x+y)xe2x89xa60.90 
when the composition of the high dielectric constant film is expressed as MxSiyO, where M, O and Si represent the metal, oxygen and silicon, respectively, and x greater than 0 and y greater than 0.
This ensures the thermal stability of the high-k gate insulating film against a heat treatment at about 900xc2x0 C. while keeping the relative dielectric constant of the high-k gate insulting film sufficient.
In the semiconductor device of the present invention, it is preferable to satisfy
0.23xe2x89xa6y/(x+y)xe2x89xa60.30 
when the composition of the high dielectric constant film is expressed as MxSiyO, where M, O and Si represent the metal, oxygen and silicon, respectively, and x greater than 0 and y greater than 0.
This ensures the thermal stability of the high-k gate insulating film against a heat treatment at about 900xc2x0 C. while keeping the reliability life of the high-k gate insulting film sufficient.
In the semiconductor device of the present invention, it is preferable to satisfy
x/(x+y)xe2x89xa70.10 
when the metal is hafnium or zirconium, and the composition of the lower barrier film is expressed as MxSiyON, where M, O, Si and N represent the metal, oxygen, silicon and nitrogen, respectively, and x greater than 0 and y greater than 0.
This ensures that the relative dielectric constant of the lower barrier film can be increased.
In the semiconductor device of the present invention, the gate electrode may be a metal gate electrode.
A first method for producing a semiconductor device of the present invention includes the steps of forming a high dielectric constant film containing a metal, oxygen and a predetermine substance on a substrate; performing a heat treatment with respect to the high dielectric constant film to diffuse silicon from the side of the substrate into the high dielectric constant film, thereby forming a silicon-containing high dielectric constant film; and forming a conductive film for serving as a gate electrode on the silicon-containing high dielectric constant film.
According to the first method for producing a semiconductor device, a predetermined substance can be desorbed from the high dielectric constant film by performing a heat treatment with respect to the high dielectric constant film containing the predetermined substance, so that silicon is diffused in the high dielectric constant film through the thus formed vacancies and thus a silicon-containing high dielectric constant film can be formed. Therefore, silicon can be contained in the high dielectric constant film efficiently, and the vacancies eventually disappear, so that the silicon-containing high dielectric constant film can become dense. The silicon-containing high dielectric constant film hardly is crystallized by a high temperature treatment in the production process, so that the silicon-containing high dielectric constant film remains mostly amorphous after a device is complete. As a result, leak current can be suppressed from occurring in the gate insulating film including the silicon-containing high dielectric constant film, that is, the high-k gate insulating film. Consequently, the thermal stability of the high-k gate insulating film can be improved, and therefore a semiconductor device having excellent heat resistance can be realized, and the process margin in the production of a semiconductor device can be increased.
In the first semiconductor method of the present invention, it is preferable the predetermined substance is hydrogen.
This ensures that silicon can be diffused in the high dielectric constant film.
It is preferable that the first semiconductor method includes forming an insulating film containing silicon, nitrogen and the predetermined substance on the substrate before the step of forming the high dielectric constant film; and that the step of performing a heat treatment with respect to the high dielectric constant film comprises diffusing silicon contained in the insulating film into the high dielectric constant film, and forming a lower barrier film by diffusing the metal contained in the high dielectric constant film into the insulating film.
This ensures that silicon can be diffused in the high dielectric constant film. Furthermore, the high dielectric constant film or the silicon-containing high dielectric constant film can be prevented from reacting with the substrate. Moreover, the lower barrier film contains the same metal as in the silicon-containing high dielectric constant film, so that the relative dielectric constant of the lower barrier film can be increased, and thus the relative dielectric constant of the gate insulting film as a whole can be increased.
In the first method for producing a semiconductor device, it is preferable that the step of forming a high dielectric constant film comprises forming a high dielectric constant film by CVD employing a source precursor containing the metal and the predetermined substance.
Thus ensures that a high dielectric constant film containing the predetermined substance is formed.
In the first method for producing a semiconductor device, it is preferable that the step of forming the high dielectric constant film includes forming the high dielectric constant film by CVD employing a source precursor containing the metal and a source gas containing the predetermined substance.
Thus ensures that a high dielectric constant film containing the predetermined substance is formed.
In the first method for producing a semiconductor device, it is preferable that the step of forming the high dielectric constant film includes forming the high dielectric constant film by PVD employing a target containing the metal in an atmosphere containing the predetermined substance.
Thus ensures that a high dielectric constant film containing the predetermined substance is formed.
A second method for producing a semiconductor device of the present invention includes the steps of forming a high dielectric constant film containing a metal, oxygen and hydrogen on a substrate; performing a heat treatment with respect to the high dielectric constant film to diffuse silicon from the side of the substrate into the high dielectric constant film, thereby forming a silicon-containing high dielectric constant film; and forming a conductive film for serving as a gate electrode on the silicon-containing high dielectric constant film.
According to the second method for producing a semiconductor device, hydrogen can be desorbed from the high dielectric constant film by performing a heat treatment with respect to the high dielectric constant film containing hydrogen, so that silicon is diffused in the high dielectric constant film through the thus formed vacancies and thus a silicon-containing high dielectric constant film can be formed. Therefore, silicon can be contained in the high dielectric constant film efficiently, and the vacancies eventually disappear, so that the silicon-containing high dielectric constant film can become dense. The silicon-containing high dielectric constant film hardly is crystallized by a high temperature treatment in the production process, so that the silicon-containing high dielectric constant film remains mostly amorphous after a device is complete. As a result, leak current can be suppressed from occurring in the gate insulating film including the silicon-containing high dielectric constant film, that is, the high-k gate insulating film. Consequently, the thermal stability of the high-k gate insulating film can be improved, and therefore a semiconductor device having excellent heat resistance can be realized, and the process margin in the production of a semiconductor device can be increased.
It is preferable that the second method for producing a semiconductor device includes forming an insulating film containing silicon, nitrogen and hydrogen on the substrate before the step of forming the high dielectric constant film; and that the step of performing a heat treatment with respect to the high dielectric constant film includes diffusing silicon contained in the insulating film into the high dielectric constant film, and forming a lower barrier film by diffusing the metal contained in the high dielectric constant film into the insulating film.
This ensures that silicon can be diffused in the high dielectric constant film. Furthermore, the high dielectric constant film or the silicon-containing high dielectric constant film can be prevented from reacting with the substrate. Moreover, the lower barrier film contains the same metal as in the silicon-containing high dielectric constant film, so that the relative dielectric constant of the lower barrier film can be increased, and thus the relative dielectric constant of the entire gate insulting film can be increased.
In the second method for producing a semiconductor device, it is preferable that the step of forming the high dielectric constant film includes forming the high dielectric constant film by CVD employing a source precursor containing the metal and hydrogen.
Thus ensures that a high dielectric constant film containing hydrogen can be formed.
In the second method for producing a semiconductor device, it is preferable that the step of forming the high dielectric constant film includes forming the high dielectric constant film by CVD employing a source precursor containing the metal and a source gas containing hydrogen.
Thus ensures that a high dielectric constant film containing hydrogen can be formed.
In the second method for producing a semiconductor device, it is preferable that the step of forming the high dielectric constant film includes forming the high dielectric constant film by PVD employing a target containing the metal in an atmosphere containing hydrogen.
Thus ensures that a high dielectric constant film containing hydrogen can be formed.
In the first or the method for producing a semiconductor device, it is preferable that the metal is hafnium or zirconium.
This ensures that the relative dielectric constant of the silicon-containing high dielectric constant film can be increased.
In the first or the second method for producing a semiconductor device, it is preferable that the method includes the step of forming an upper barrier by nitriding a surface of the silicon-containing high dielectric constant film between the step of performing a heat treatment with respect to the high dielectric constant film and the step of forming a conductive film.
This prevents the gate electrode material and the high dielectric constant film material from being diffused to each other. Moreover, the upper barrier film contains the same metal as in the high dielectric constant film, so that the relative dielectric constant of the upper barrier film can be increased, and thus the relative dielectric constant of the entire gate insulting film can be increased.
In the first or the second method for producing a semiconductor device, it is preferable that the method includes the step of forming an upper barrier by nitriding a surface of the high dielectric constant film between the step of forming a high dielectric constant film and the step of performing a heat treatment with respect to the high dielectric constant film.
This prevents the gate electrode material and the high dielectric constant film material from being diffused to each other. Moreover, the upper barrier film contains the same metal as in the high dielectric constant film, so that the relative dielectric constant of the upper barrier film can be increased, and thus the relative dielectric constant of the entire gate insulting film can be increased.
In the first or the second method for producing a semiconductor device, it is preferable that the temperature for the heat treatment in the step of performing the heat treatment with respect to the high dielectric constant film is 600xc2x0 C. or more and 850xc2x0 C. or less.
This ensures that the predetermined substance or hydrogen can be desorbed from the high dielectric constant film, and that silicon can be diffused in the high dielectric constant film.
In the first or the second method for producing a semiconductor device, it is preferable to satisfy Txe2x89xa66.69xc2x7y/(x+y)+749.4, when the composition of the silicon-containing high dielectric constant film is expressed as MxSiyO, where M, O and Si represent the metal, oxygen and silicon, respectively, and x greater than 0 and y greater than 0, and the maximum temperature in the production process is expressed as T [xc2x0 C.].
This ensures the thermal stability of the high-k gate insulating film having the silicon-containing high dielectric constant film.
In this case, it is preferable that the gate electrode is made of a material containing silicon, and y/(x+y)xe2x89xa60.30 is satisfied.
This enables a sufficient reliability life for the high-k gate insulating film having the silicon-containing high dielectric constant film.
In the first or the second method for producing a semiconductor device, it is preferable that the gate electrode is a metal gate electrode, and the method includes the step of performing a heat treatment with respect to the substrate after the step of forming a conductive film.
This allows the defects in the high-k gate insulating film having the silicon-containing high dielectric constant film to be reduced further.